Microdomain regulation of Ca2+ release in cardiac physiology and disease

由心律失常引起的猝死是心脏病最常见的后果，通常是由异常冲动形成造成的。这种触发的活性与肌浆网（SR） Ca2+释放异常有关，是儿茶酚胺能多态性室性心动过速（CPVT）的标志。ryanodine受体（RyR2）或calsequestrin (Casq2)（主要的sr内Ca2+结合蛋白）的cpvt相关突变导致RyR2泄漏并使这些患者易患心律失常。房颤是CPVT的另一个常见发现，表明CPVT中的Ca2+处理不当并不孤立于心室。尽管CPVT对Ca2+通道和/或β -受体阻滞剂有很高的反应，但难治性病例通常需要基于Na+通道抑制剂的治疗。然而，钠+内流和Ca2+处理干扰之间的关系在CPVT心律失常之前仍然知之甚少。申请人已经开发了一种实验系统，使用各种小鼠CPVT模型，将细胞水平上的Ca2+处理信息与组织中的电生理表型相结合。申请人计划研究Na+通道亚群（神经元Na+通道；nNav）通过微域Na+/Ca2+信号传导参与致心律失常的异常Ca2+释放的假设。具体来说，该建议将在指导阶段（K99）解决以下目标：1)阐明亚区域特异性Na+/Ca2+信号在Ca2+依赖性心房和室性心律失常的发生中对异常Ca2+释放的分子和亚细胞后果。在这里，我们将测试亚域特异性Na+/Ca2+信号传导有助于心律失常异常Ca2+释放的假设，同时试图确定局部Na+/Ca2+亚域信号传导的分子决定因素。2)明确Na+/Ca2+信号在组织范围内异常Ca2+释放同步中的作用。这些翻译研究将验证亚域特异性Na+/Ca2+信号传导促进心肌同步异常Ca2+释放和促进随后的异位活动在完整心室组织的假设。3)验证的适用性

DESCRIPTION (provided by applicant): Project Summary Sudden death resulting from cardiac arrhythmias is the most common consequence of cardiac disease and is oftena result of abnormal impulse formation. Such triggered activity are associated with abnormal Ca2+ release from the sarcoplasmic reticulum (SR) and are a hallmark of catecholaminergic polymorphic ventricular tachycardia (CPVT). CPVT-associated mutations in the ryanodine receptors (RyR2) or calsequestrin (Casq2), the major intra-SR Ca2+ binding protein render the RyR2 leaky and predispose these patients to arrhythmias. Atrial fibrillation is an another common finding in CPVT, indicating that Ca2+ mishandling in CPVT is not isolated to the ventricles. Despite high response of CPVT to Ca2+ channel- and/or beta-blockers, refractory cases often require Na+ channel inhibitor based therapy. However, the relationship between Na+ influx and disturbances in Ca2+ handling immediately preceding arrhythmias in CPVT remains poorly understood. The applicant has developed an experimental system using various murine models of CPVT that integrates information of Ca2+ handling at the cellular level with the electrophysiologic phenotype in tissue. The applicant plans to investigate the hypothesis that subpopulation of Na+ channels (neuronal Na+ channels; nNav) contribute to arrhythmogenic aberrant Ca2+ release through the microdomain Na+/Ca2+ signaling. Specifically the proposal will address the following aims during the mentored phase (K99): 1) Elucidate the molecular and subcellular consequences of subdomain-specific Na+/Ca2+ signaling on aberrant Ca2+ release in the genesis of Ca2+ -dependent atrial and ventricular arrhythmias. Here we will test the hypothesis that subdomain-specific Na+/Ca2+ signaling contributes to arrhythmogenic aberrant Ca2+ release while attempting to identify the molecular determinants of local Na+/Ca2+ subdomain signaling. 2) Define the role of Na+/Ca2+ signaling in tissue wide aberrant Ca2+ release synchronization. These translational studies will test the hypothesis that subdomain-specific Na+/Ca2+ signaling facilitates myocardial synchronization of aberrant Ca2+ release and promotes subsequent ectopic activity in intact ventricular tissue. 3) Validate the applicability of Na+/Ca2+ signaling to in vivo settings. During the independent phase (R00) the proposal will: 1) Investigate the role of subdomain-specific Na+/Ca2+ signaling on aberrant Ca2+ release in the genesis of atrial arrhythmias. 2) Examine the regional heterogeneities of the subdomain-specific Na+/Ca2+ signaling in atrial aberrant Ca2+ release synchronization. 3) Validate the therapeutic potential of perturbation of Na+/Ca2+ signaling in settings of atrial arrhythmias and translate the applicability to animal models of acquired Ca2+-mediated arrhythmias. The mechanistic and pharmacological insights gained on the cellular as well as on tissue levels will offer a mechanism-based therapeutic approach that will be tested in vivo. Furthermore, these studies will determine whether such arrhythmogenic mechanism(s) is/are applicable to a clinically-relevant model of Ca2+-mediated arrhythmias. A long term goal of this study is to better understand the cellular and molecular mechanisms of Ca2+-mediated arrhythmogenesis.